1. Field of the Invention
The present invention relates generally to printing presses and more particularly to a device and method for providing a liquid to a cylinder of a printing press.
2. Background Information
Offset lithographic printing presses, for example, have a blanket cylinder for transferring images from a printing plate to a web of material, such as paper. Blankets on the blanket cylinder typically have a rubber outer print layer.
Especially after continued use, blankets in the printing press accumulate foreign matter such as dried ink, lint, dust, clay, dirt and the like which should be periodically removed by cleaning. When changing a print job, it may be desirable that the blankets are cleaned. Lack of proper cleaning can lead to poor print quality and reduced press productivity.
U.S. Pat. No. 5,257,578 discloses an automatic cleaning device for cleaning blankets in a web fed offset lithographic printing press. A brush roller is selectively applied to the blanket for removing foreign matter from the blanket. A blanket wash solution is applied to the brush roller in order to improve the cleaning of the blanket. U.S. Pat. No. 5,257,578 is hereby incorporated by reference herein.
The blanket wash solution for such devices is typically applied by a spray bar, which sprays a cleaning solution or solvent through a line of holes along the entire width of the brush. The spray bar cleaning solution thus is applied through the brush to the entire blanket when the blanket is cleaned. If the web in the printing press is the same width as the blanket, the cleaning of the entire blanket width is desirable.
However, it is often desired to print narrower web widths with an offset printing press. For example, even though a printing press could print a 57 inch web width, it may be desired to use the same press to print solely a 30 inch wide web, depending on the type of printed products desired. In this case, spray bar blanket wash systems will still spray cleaning solution across the entire 57 inch brush and blanket cylinder width. Since many cleaning systems rely on the web to remove the debris during the wash, the narrow 30 inch web will not readily remove debris and used cleaning solution from areas beyond the web width. Moreover, in the areas beyond the web width, the cleaning solution is still being applied and is not carried away by the web. In other words, a section of the blanket cylinder 27 inches wide is still receiving cleaning solution, even though no web is in that area.
The application of cleaning solution beyond the web width causes excess waste of cleaning solution or solvent, as the solvent exits as waste and is not reused. The disposal of the solvent, which may be environmentally sensitive material, can be expensive.
Moreover, the excess solvent can work its way into the narrow web during a print run, breaking down ink on the web and leading to print quality degradation. This degradation can cause paper waste, as the resulting printed products often have a washed out look or are unreadable and must be discarded.
European Patent Application No. 0 618 074 A2 purports to disclose a printing machine spraying device for spraying fluid having two emitters movable axially with respect to a printing cylinder. The fluid can be used to clean a blanket, and the emitters can be automatically controlled so as to be moved axially over the entire width or part of a desired width of the blanket cylinder, depending on how wide the printed material is.
The device of the ""074 European patent application has a disadvantage in that the desired blanket width is not sprayed at one time, but rather in portions as the emitters move axially, thus requiring more time to coat the desired width. Moreover, the movement and control of the emitters requires a complex arrangement, which can be subject to malfunction or fouling.
An object of the present invention is to provide for a reliable and efficient device and method for providing cleaning or other solution to a cylinder or part of a printing press.
The present invention provides a device for providing cleaning or other solution in a printing press comprising:
a spraying device, the spraying device having a liquid exit disposed along a width of the spraying device for delivering a liquid to a press component; and
a spray shield selectively covering at least one part of the liquid exit so as to block delivery of the liquid through the at least one part to the press component.
The present invention permits instantaneous delivery of liquid, such as a cleaning solution, to the press component through the liquid exit, over variable widths, for example corresponding to a web width.
Preferably, the spraying device is a spray bar, the spray bar being at least as wide as the press component.
The press component preferable is a blanket cleaning brush or a blanket of an offset lithographic printing press.
Preferably, the liquid exit is a plurality of holes, and the at least one part is at least one of the holes disposed at one or both ends of the spray bar.
The spray shield preferably is at least one cylinder rotatable with respect to the spraying device, the cylinder having at least one aperture having a variable width.
In a first embodiment, the spray shield includes two rotatable cylinders, each at one end of the spray bar. Each has an aperture with a sloped or angled side for selectively covering a part of the liquid exit so as to narrow the effective spray area. The middle of the spray bar may remain unaffected by the cylinders. Alternately, if a narrow web is run at a side of the press, and not exactly in the middle, the spray shield may be a single cylinder with a sloped aperture can be provided on one side.
In alternate embodiments, the spray shield may have a single cylinder with a single aperture having sloped ends, or with a plurality of apertures with different widths.
The spraying device preferably is stationary, while the cylinder rotates around the spray bar. Preferably, the rotation is performed manually. However, the rotation may be effected by an air cylinder fixed at one end to the spray bar and at the other end to a follower which fits in a helical slot in the interior of the spray shield. The air cylinder motion thus rotates the spray shield. Most preferably, two air cylinders are provided, one having double the stroke length of the other, so that four equally spaced positions can be attained.
Preferably, a collection device collects the blocked liquid from the spray shield and returns it to a cleaning fluid reservoir.
The present invention also provides an offset lithographic printing unit with a plate cylinder, a blanket for contacting a plate on the plate cylinder and a blanket cleaning device. The blanket cleaning device includes a spraying device with a liquid exit disposed along a width of the spraying device for delivering a liquid, directly or indirectly, to the blanket, and a spray shield selectively covering at least one part of the liquid exit so as to block delivery of the liquid through the at least one part to the blanket.
Also provided is a method for providing cleaning or other fluid to a printing press component comprising the steps of spraying a fluid over a fixed width of a press component, and blocking part of the fluid over a part of the fixed width so that the part of the fluid does not reach the press component.